Thermal deformation of plastic
Depending on what you are trying to accomplish (a sketch of the desired result might help) and how much patience you have, you may want to use either sculpt mode or proportional editing in edit mode.
Sculpt mode is helpful if you have a large number of vertices, or if you want to deform meshes with natural strokes of the mouse. If you need more precise control, proportional editing allows you to move individual verts/edges/faces around, and the neighboring geometry will &quot;stretch&quot; in similar ways. Both of these allow you to adjust the radius of effect.